The golden hamster (Mesocricetus auratus) is being used as a possible model for the study of immunity to human kala-azar. Studies in our laboratory indicate that hamsters drug-cured of active Leishmania donovani infections or infected subcutaneously with L. donovani parasites possess significant resistance to either intracardial or cutaneous challenge infections. It is proposed to study various aspects of the immune response to include the reproductive rate of parasites in immune versus normal hamsters and the ability of macrophages from these hamsters to inhibit L. donovani reproduction or metabolism in vitro. In addition, it is proposed to study the interactions of parasite antigens with host lymphoid cells with the purpose of identifying factors which may contribute to hypergammaglobulinemia during infection.